Enantioselective Alkynylation Reactions to Substituted Benzaldehyde and Salicylaldehyde Derivatives: The Effect of Substituents upon the Efficiency and Enantioselectivity

摘要

Asymmetric alkynylation reactions to mono-, di-, and trisubstituted aromatic aldehydes have been accomplished in good yields and with a range of selectivities. For salicylaldehyde derivatives both the yield and the enantioselectivity of the alkynylation reaction appears to depend not only upon the electron-donating/ electron-withdrawing nature of substituents but also upon their position in the ring relative to the carbonyl. For benzaldehyde derivatives this observation is exemplified with nitrobenzaldehyde wherein asymmetric alkynylation with 3-nitrobenzaldehyde occurs in virtually quantitative yield and enantioselectivity. In contrast our attempts at asymmetric alkynylations with 4-nitrobenzaldehyde failed.